1. Field of the Invention
The present invention relates to a modified pigment having a reduced conductivity increase as well as inkjet ink compositions comprising these modified pigments.
2. Description of the Related Art
Methods for the preparation of modified pigment products have been developed which can provide a pigment with a variety of different attached functional groups. For example, U.S. Pat. No. 5,851,280 discloses methods for the attachment of organic groups onto pigments including, for example, attachment via a diazonium reaction wherein the organic group is part of the diazonium salt.
Other methods to prepare modified pigments, including those having attached polymeric groups, have also been described. For example, PCT Publication No. WO 01/51566 discloses methods of making a modified pigment by reacting a first chemical group and a second chemical group to form a pigment having attached a third chemical group. Also, U.S. Patent Application Publication No. 2007/0100024 discloses modified colorants comprising a colorant having attached at least one organic group, wherein the organic group has a defined calcium index values. Specific embodiments of the organic groups are described, including organic groups comprising at least one geminal bisphosphonic acid group, partial esters thereof, or salts thereof. In addition, U.S. Pat. Nos. 5,672,198, 5,922,118, 6,042,643, and 6,641,656 disclose modified pigments having various attached groups, including phosphonic acid groups.
Ink compositions, including inkjet inks, containing these modified pigments have also been described, and these inkjet inks have been shown to have good overall performance properties. In general, the properties of these inkjet ink compositions depend on a variety of factors, including pigment type, type of attached group, and types of additives, and thus, modified pigments can be tailored to meet the needs of various types of inkjet ink compositions, including those useful for both thermal and piezo inkjet ink printers.
However, as the requirements of the various inkjet ink industries become more demanding, there remains a need for modified pigments having improved performance properties, such as low conductivity for piezo printers, particularly those using shear mode printheads, thereby providing advantageous alternatives to previous modified pigments.